1. Field of Invention
The present invention relates to a transistor. More particularly, the present invention relates to a thin film transistor.
2. Description of Related Art
Digital circuit integration is very popular in semiconductor device manufacturing field, and enables the electronic and information industry to progress rapidly as well. In recent years, applications of the digital technology have been extended to some analog fields. Traditionally, an integrated circuit has only one single dielectric layer. However, as the design of the integrated circuit becomes more and more complicated, one single dielectric layer cannot meet the requirement of a new generation integrated circuit. In a conventional manufacturing process of a high-voltage component, a relatively thick gate oxide layer needs to be developed for sustaining a high pressure working environment.
In the design of a thin-film transistor, a gate electrode and a source/drain electrode can be either partially overlapped or separated without overlapping. If the electrodes are separated without overlapping, a uniformity problem may arise due to poor alignment during an etching process, which affects electrical properties of the thin film transistor, and an allowable gate line width due to the limit of minimum resolution.
On the other hand, if in the thin-film transistor the source electrode and the gate electrode or the drain electrode and the gate electrode are made to be overlapped, although the photocurrent problem can be prevented, however, yet the overlapped electrodes will produce stray capacitance, which slows down the transistor operation speed. In addition, some material layers of the thin film transistor require to be formed by a continuous film-forming process, in which case the thickness of the dielectric layer needs to be increased to reduce the stray capacitance, the conduction current will be reduced due to the increased thickness of the dielectric layer, thus affecting the transistor performance.